1. The Field of the Invention
The present invention relates to a modular prosthesis for replacing a portion of a bone having an articulating end and the methods of assembly and use thereof.
2. The Relevant Technology
Illustrated in FIG. 1 is a hip joint 10 by which a femur 12 rotatably couples with pelvic bone 14. Femur 12 comprises an articulating end 16, an elongated shaft 18, and a metaphyseal equivalent 20 which transitions therebetween. One occasion, it is necessary to replace the hip joint due to injury or other failure of the structure. Replacement of the hip joint typically comprises resecting articulating end 16 across metaphyseal equivalent 20 so as to expose the intramedullary canal extending through shaft 18. The distal end of a prosthesis is then inserted into the intramedullary canal of femur 12 so as to secure the prosthesis in place. Projecting from the prosthesis is a spherical head. The spherical head is configured to mate with a complimentary prosthetic or natural acetabulum or socket formed on pelvic bone 14.
In view of the fact that individuals come in all different sizes and shapes, it is of ten difficult to precisely fit and place the prosthesis for optimal function. Modular orthopedic prostheses have thus been provided which assist in optimizing fit and placement by allowing components of the prosthesis to be exchanged for different sizes and configurations. That is, by selecting independent modular components to construct a complete prosthesis, custom fitting of a patient's specific anatomy or specific bone condition can be accomplished.
Several attachment mechanisms are known in the art for connecting the components of a modular prosthesis. Generally, any two modular components are connected by one contiguous interface. Even three-piece modular connections typically rely on only one contiguous connection interface between any two modular components.
Because of the high physiological loads borne by the skeletal structure, orthopedic prostheses are subject to high bending, shear, and torsional loads. Where a single contiguous connection is used to connect components of a modular prosthesis, the applied loads can be localized, thereby increasing the failure at that point. It would therefore be an improvement in the art to provide modular orthopedic prostheses that can better withstand the mechanical service loads by better distributing the loads acting upon the prosthesis.
Furthermore, one of the advantages of modular orthopedic prostheses is the capacity to select, at the time of surgery, a desired orientation between modular components. Many modular connections known in the art do not facilitate a state of partial assembly that closely replicates the final longitudinal configuration of the prosthesis, where, in the state of partial assembly, the modular components can be freely rotated with respect to each other. It would therefore be another improvement in the art to provide modular prostheses that would accommodate a state of partial assembly that closely replicates the longitudinal configuration of the prosthesis while permitting free relative rotation between the modular components.